This invention relates to a granulating apparatus or pelletizer for manufacturing granular particles like those of medicine, instant soup, livestock feed, etc., from powdery raw material.
A granulating apparatus or pelletizer known to date comprises means for carrying out the steps of spraying a binder solution on raw particles to bond them together, drying the bonded granules, and later again spraying the binder solution on the dried bonded granules. In the granulating or pelletizing chamber of the conventional granulating apparatus or pelletizer, involving the above-mentioned steps, hot air is introduced only upwardly from below a fluidized bed or layer of raw particles for their drying. The raw particles constituting the fluidized bed are kept floating in such a condition that a balance is established between the force of heated air blowing particles upward and the gravitational force letting the particles fall. In this case, those particles which have a great apparent density, that is, a heavier weight, float in the lower portion of the fluidized bed, whereas those particles of small apparent density, that is, a lighter weight, remain in the upper portion of the fluidized bed. The particles constituting the upper portion of the fluidized bed, which are wetted by binder solution, sprayed by an atomizer, increase in apparent density and fall downward and are handled as bonded heavy particles. When the particles wetted by a binder solution are dried by an upward flowing hot air stream, the solvent of the binder solution is evaporated, thereby reducing the apparent density of the particles. As a result, the particles which are now rendered light move upward. The rising particles are again wetted by the binder solution to increase weight and bond with other adjacent particles while falling downward. As described above, raw particles in the fluidized bed are repeatedly wetted by the binder solution and bonded with other adjacent particles to gradually grow into large granules having prescribed measurements.
A granulating apparatus or pelletizer known to date is only a batch type. Namely, the conventional granulating apparatus or pelletizer is characterized in that when raw particles grow into granules having a prescribed diameter, the apparatus is brought to rest to remove all the particles from a pelletizer tank. However, the failure to apply a continuous process is for the reason that when particles are taken out during operation from the upper portion of a fluidized bed held in the pelletizer tank, insufficiently pelletized particles are undesirably withdrawn; and when particles are removed during the operation from the lower portion of the fluidized bed, moistened particles still wet from the binder solution are discharged; namely, it has been impossible to continuously take out particles having a prescribed diameter from the pelletizer. Therefore, the conventional granulating apparatus or pelletizer is accompanied with the drawback that the batch process has reduced production efficiency.